Pressostat

ABSTRACT

The invention is a pressostat assembly which includes two bellows, one inside the other, which have fluid communication. Both bellows are fixedly attached to a rod form of operating member and the outer bellows operates to impart a closing movement to the operating member if the inner bellows should develop a leak. The effective cross sectional area of the outer bellows is larger than that of the inner bellows. The rod form of operation member is provided with a passage for filling or evacuating a protective chamber surrounded by the protective bellows.

Kraemer Oct. 23, 1973 [54] PRESSOSTAT 2,718,896 9/1955 Jones 92/37 X 2,761,927 9/1956 Sz ulski 200/83 C [75] lnvenm Kramer Nordborg 2,988,282 6/1961 Hd t t enroth 92 35 x Denmark 3,055,219 9/1962 Wilson et a1 73/410 [73] Assignee: Danfoss A/S, Nordborg, Denmark I Primary ExaminerMartin P. Schwadron [22] Filed: July 3, 1972 Appl. No.: 268,608

Foreign Application Priority Data July 3, 1971 Germany P21 33 216.1

References Cited UNITED STATES PATENTS 2/1943 Thompson et al. 92/35 X 12/1953 Strobell 92/35 X v Assistant Examiner-Abe Hershkovitz Attorney-Wayne B. Easton [57] ABSTRACT The invention is a pressostat assembly which includes two bellows, one inside the other, which have fluid communication. Both bellows are fixedly attached to a rod form of operating member and the outer bellows operates to impart a closing movement to the operating member if the inner bellows should develop a leak. The effective cross sectional area of the outer bellows is larger than that of the inner bellows. The rod form of operation member is provided with a passage for filling or evacuating a protective chamber surrounded by the protective bellows.

4 Claims, 1 Drawing Figure PRESSOSTAT The invention relates to a pressostat assembly comprising an actuating element for operating a switch. The assembly includes inner and outer bellows operatively connected to said actuating element, a spring counteracting the pressure in the actuating element, and a switching element which responds when a limit valve for pressure is exceeded in the actuating element. The actuating element is also referred to herein as a working element.

The outer bellows has a protective function and the inner bellows is the operating bellows for normal operation. The operating bellows is acommodated in an enclosed protective chamber, part of the outer wall of which is formed by the protective bellows which likewise counteracts the spring and which actuates the switching element when a limit value for pressure in the protective chamber, that is lower than the limit value for pressure in the working element, is exceeded. In this arrangement it is advantageous if the protective bellows surrounds the operating bellows and has a larger effective pressure face than the latter and is connected to the outlet control member of the working element. The outlet control member only need bear against the operating bellows in a mechanically positivemanner.

A pressostat of this kind actuates the switching element not only during the normal course of operations, but also very soon after the occurrence of damage to the pressostat, particularly if the operating bellows develops a leak. If the pressure in the enclosed protective chamber is below that of the surrounding atmosphere, the additional bellows is also monitored. Thus a selfmonitoring pressostat of very simple construction is provided.

In accordance with the present invention, the construction of a pressostat of this kind is provided with a closed passage in the outlet control member of the working element for the purpose of filling or evacuating the protective chamber surrounded by the protective bellows.

Since the outlet control member has to be machined in any case, no difficulty is presented in also providing it with the filling or' evacuating passage. The mouth of the passage which as to be closed after filling or evacuation is located in a readily accessible position. In particular, there is no need for a passage of this kind in the casing at the opposite end of the additional bellows, and the casing can therefore be correspondingly small.

A very simple construction is obtained if the passage is formed by an axial bore leading to the free end-face of the outlet control member, and by a transverse bore. These two passages can be formed without great expense when machining the outlet control member.

Expediently, a copper tube is soldered into the axial bore, and after the protective chamber has been filled or evacuated, this tube is closed by soldering. A very short length of copper tube suffices. Closing is facilitated by the double soldering.

Furthermore, the outlet control member may have a flange that is located near the outer face of the additional bellows, and a cover cap forming a bearing can be mounted on this flange. The soldered point, forming a seal for the copper tube, is thus additionally protected.

The invention will now be described in greater detail by reference to an embodiment illustrated in the drawing, which shows diagrammatically a section through a pressostat in accordance with the invention.

An insert 3 forming part of a pressostat 4 is introduced by means of a port 5 into a wall 1 of a container 2 of equipment through which refrigerant passes, and the insert is held in position by means of a nut 6. The port contains a connecting bore 7 which leads to the working element 8. This element is bounded by an outer wall 9 of the insert 3, a tubular bellows 10 having a pressure face 11, the inner end-face 12 of the insert 3, and a ring 13 which is connected to the operating bellows l0 and is secured to the wall 9 by soft soldering. An outlet control member 14 in the form of a spindle acts on the lever 15 which pivots about a pin 16. The lever is biased by a rated-value spring 17 which is held by a preferably adjustable backing element 18. The free end of the lever 15 actuates a switching element 19 which in the present case is the plunger 20 of a micro-switch.

The working element 8 is surrounded by a protective chamber 21 which is bounded by an additional bellows 22 having a pressure face 23, the side wall 9 of the insert 3 and a flange 24 of the insert 3, which flange is silver-soldered to said insert. The additional bellows 22 is soft-soldered to the flange 24 at 25, and is silversoldered to the outlet control member 14 at 26. The size of the pressure face 23 is a multiple of that of the pressure face 11. During normal operation, the pres- I sure in the enclosed protective chamber 21 is below that of the atmosphere.

The outlet control member 14 has a passage 27 which consists of a bore 28, coaxial with said member, and of a transverse bore 29. A copper pipe 30 is secured in the free end of the passage 27 at 31 by softsoldering. After the protective chamber 21 has been filled or evacuated, the mouth of the copper tube 30 is squeezed up at 32 and sealed by soft-soldering. The control member 14 has a flange 33 which lies on the pressure face 23 of the additional bellows 22. Mounted on this flange is a cover cap 34 which terminates in a point forming a bearing 35 for the lever 15; the soldered point 32 is protected within this cap.

The pressostat 4 operates in the following manner. When the pressure in the container 2 of the equipment rises, this pressure also acts upon the working element 8. If this pressure exceeds a predetermined level, which is above the normal operating values, the operating bellows l0 displaces the outlet control member 14, thereby overcoming the force of the spring 17. This causes the lever 15 to swing in the counter-clockwise direction, and the micro-switch 19 is actuated. This can be used for switching off the feed unit of the equipment, eg ,of a'refrigerating machine.

If the operating bellows 10 develops a crack, the same pressure as that in the working element 8 is established in the protective chamber 21 after a short time. As a result of the large pressure face 23, a pressure that is only slightly below that occurring in normal operation suffices to overcome the force of the rated-value spring 17 and to actuate the micro-switch 19. Development of a leak in the working element 8 therefore results in the feed unit of the equipment being switched off.

If the additional bellows 22 develops a crack, atmospheric pressure develops in the protective chamber 21 after a short time, whereas sub-atmospheric pressure normally is present in this chamber. As a result of this rise in pressure, the lever is again swung, thereby overcoming the force of the rated-value spring 17, and the micro-switch 19 is actuated.

The pressostat is therefore not only a safety means which monitors excessive rises in pressure in the equipment, but it also prevents the unintentional discharge of the pressure medium from the equipment and rapidly switches off when a leak develops in the working element. Furthermore, those parts used for this additional function are so designed as to be self-monitoring.

I claim:

1. A pressostat assembly comprising a housing having wall means which defines a chamber, said housing defining a port having fluid communication with said" thereof being fixedly attached relative to said housing to form'a fluid tight sub-chamber having direct fluid communication with said port, said second pressure face being smaller than said first pressure face, said control member having a passage for filing and evacuating said protective chamber.

2. A pressostat assembly according to claim 1 wherein said passage comprises an axial bore opening tothe outside of said control member and a connecting transverse bore having fluid communication with said protective chamber.

3. A pressostat assembly according to claim 2 including a copper. tube attached to said control member in fluid communication with said passage, said tube being sealed by soldering.

' 4. A pressostat assembly according to claim 3 wherein said control member has a flange fixedly attached' to said first pressure face, and cap means attached to said flange in surrounding relation to said copper tube. 

1. A pressostat assembly comprising a housing having wall means which defines a chamber, said housing defining a port having fluid communication with said chamber, a first bellows surrounding said wall means to form a protective chamber with the lower end thereof fixedly attached to said housing and the upper end thereof forming a first movable pressure face, a control member attached to said pressure face and extending into said chamber, a second bellows surrounding said control member with the lower end thereof forming a second movable pressure face and the upper end thereof being fixedly attached relative to said housing to form a fluid tight sub-chamber having direct fluid communication with said port, said second pressure face being smaller than said first pressure face, said control member having a passage for filing and evacuating said protective chamber.
 2. A pressostat assembly according to claim 1 wherein said passage comprises an axial bore opening to the outside of said control member and a connecting transverse bore having fluid communication with said protective chamber.
 3. A pressostat assembly according to claim 2 including a copper tube attached to said control member in fluid communication with said passage, said tube being sealed by soldering.
 4. A pressostat assembly according to claim 3 wherein said control member has a flange fixedly attached to said first pressure face, and cap means attached to said flange in surrounding relation to said copper tube. 